.parent {
    width: 300px;
    background: green;
    border: 1px solid;
    /* overflow: hidden; */
}

.child1 {
    width: 100px;
    height: 100px;
    background: pink;
    float: left;
}

.child2 {
    width: 200px;
    height: 50px;
    background: red;
}

.child3 {
    width: 220px;
    height: 30px;
    background-color: aqua;
    clear: both;
}